Monitoring of Distributed Power Harvesting Systems Using DC Power Sources

ABSTRACT

A monitoring system and method for monitoring performance of individual powers sources in a distributed power source system. A monitoring module is coupled to each of the power sources, or to each string of serially connected power sources, to monitor and collect data regarding current, voltage, temperature and other environmental factors at the power source. The collected data is transmitted over a power line to a central analysis station for analysis. Data collected from each source indicates malfunction or degradation at the source. Comparison of data collected from adjacent sources filters for environmental factors impacting neighboring sources such as cloudy days for a solar panel. Comparison of data collected from the same source at different times indicates soiling or degradation of the source with time or periodic events such as a moving shade from an adjacent building.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application a continuation of U.S. patent application Ser. No.13/901,890 filed May 24, 2013, titled “Monitoring of Distributed PowerHarvesting Systems Using DC Power Sources,” which is a continuation ofU.S. patent application Ser. No. 11/951,419 filed Dec. 6, 2007, titled“Monitoring of Distributed Power Harvesting Systems Using DC PowerSources”, which claims priority to U.S. Provisional Patent Applications,Ser. No. 60/868,851, filed Dec. 6, 2006, and titled “Distributed SolarArray Monitoring, Management and Maintenance,” Ser. No. 60/868,893,filed Dec. 6, 2006, and titled “Distributed Power Harvesting System forDistributed Power Sources,” 60/868,962, filed Dec. 7, 2006, and titled“System, Method and Apparatus for Chemically Independent Battery,” Ser.No. 60/908,095, filed Mar. 26, 2007, and titled “System and Method forPower Harvesting from Distributed Power Sources,” and Ser. No.60/916,815, filed May 9, 2007, and titled “Harvesting Power from DirectCurrent Power Sources.” The entire contents of the above-identifiedapplications are incorporated herein by reference. Further, thisapplication is related to ordinary U.S. patent application Ser. No.11/950,224, filed Dec. 4, 2007, titled “Current Bypass for DistributedPower Harvesting Systems Using DC Power Sources,” patent applicationSer. No. 11/950,271, filed Dec. 4, 2007, titled “Distributed PowerHarvesting Systems Using DC Power Sources,” patent application Ser. No.11/950,307, filed Dec. 4, 2007, titled “A Method for Distributed PowerHarvesting Using DC Power Sources,” “Removable Component Cartridge forIncreasing Reliability in Power Harvesting Systems,” and “Battery PowerDelivery Module,” that are filed in at the U.S. Patent and TrademarkOffice on Dec. 6, 2007 and incorporates the entire content of theseapplications by this reference.

BACKGROUND

1. Field of the Invention

The field of the invention generally relates to management ofdistributed DC power sources and, more particularly, to monitoring ofdistributed DC power sources, such as solar cell array, fuel cells,batteries, and similar applications.

2. Related Arts

The recent increased interest in renewable energy has led to increasedresearch in systems for distributed generation of energy, such asphotovoltaic cells (PV), fuel cells, batteries (e.g., for hybrid cars),etc. Various topologies have been proposed for connecting these powersources to the load, taking into consideration various parameters, suchas voltage/current requirements, operating conditions, reliability,safety, costs, etc. For example, most of these sources provide lowvoltage output (normally lower than 3V), so that many of them need to beconnected serially to achieve the required operating voltage.Conversely, a serial connection may fail to provide the requiredcurrent, so that several strings of serial connections may need to beconnected in parallel to provide the required current.

It is also known that power generation from each of these sourcesdepends on manufacturing, operating, and environmental conditions. Forexample, various inconsistencies in manufacturing may cause twoidentical sources to provide different output characteristics.Similarly, two identical sources may react differently to operatingand/or environmental conditions, such as load, temperature, etc. Inpractical installations, different source may also experience differentenvironmental conditions, e.g., in solar power installations some panelsmay be exposed to full sun, while others be shaded, thereby deliveringdifferent power output. While these problems and the solutions providedby the subject invention are applicable to any distributed power system,the following discussion turns to solar energy so as to provide betterunderstanding by way of a concrete example.

A conventional installation of solar power system 10 is illustrated inFIG. 1. Since the voltage provided by each individual solar panel 101 islow, several panels are connected in series to form a string of panels103. For a large installation, when higher current is required, severalstrings 103 may be connected in parallel to form the overall system 10.The solar panels are mounted outdoors, and their leads are connected toa maximum power point tracking (MPPT) module 107 and then to an inverterbox 104. The MPPT 107 is typically implemented as part of the inverter104.

The harvested power from the DC sources is delivered to the inverter104, which converts the fluctuating direct-current (DC) intoalternating-current (AC) having a desired voltage and frequency, which,for residential application, is usually 11OV or 220V at 60 Hz or 220V at50 Hz. The AC current from the inverter 104 may then be used foroperating electric appliances or fed to the power grid. Alternatively,if the installation is not tied to the grid, the power extracted fromthe inverter may be directed to a conversion and charge/dischargecircuit to store the excess power created as charge in batteries. Incase of a battery-tied application, the inversion stage might be skippedaltogether, and the DC output of the MPPT stage 107 may be fed into thecharge/discharge circuit.

FIG. 2 illustrates one serial string of DC sources, e.g., solar panels201 a-201 d, connected to MPPT circuit 207 and inverter 204. The currentversus voltage (IV) characteristics are plotted (21Oa-21Od) to the leftof each DC source 201. For each DC source 201, the current decreases asthe output voltage increases. At some voltage value the current goes tozero, and in some applications may assume a negative value, meaning thatthe source becomes a sink. Bypass diodes are used to prevent the sourcefrom becoming a sink. The power output of each source 201, which isequal to the product of current and voltage (P=I*V), varies depending onthe voltage drawn from the source. At a certain current and voltage, thepower reaches its maximum. It is desirable to operate a power generatingcell at this maximum power point. The purpose of the MPPT is to findthis point and operate the system at this point so as to draw themaximum power from the sources.

Various environmental and operational conditions impact the power outputof DC power sources. For example, the solar energy incident on variouspanels, ambient temperature and other factors impact the power extractedfrom each panel. Depending on the number and type of panels used, theextracted power may vary widely in the voltage and current. Changes intemperature, solar irradiance and shading, either from near objects suchas trees or far objects such as clouds, can cause power losses. Ownersand even professional installers find it difficult to verify the correctoperation of the system. With time, many more factors, such as aging,dust and dirt collection and module degradation affect the performanceof the solar array.

Data collected at the inverter 104 is not sufficient to provide propermonitoring of the operation of the system. Moreover, when the systemexperiences power loss, it is desirable to ascertain whether it is dueto environmental conditions or from malfunctions and/or poor maintenanceof the components of the solar array. Furthermore, it is desirable toeasily locate the particular solar panel that may be responsible for thepower loss. However, to collect information from each panel requiressome means of communication to a central data gathering system. The datagathering system needs to be able to control data transmission, avoidtransmission collisions, and ascertain each sender of data. Such arequirement can be most easily accomplished using a duplex transmissionmethod. However, a duplex transmission method requires additionaltransmission lines and complicates the system. On the other hand,one-way transmission is prone to collisions and makes it difficult tocompare data transmitted from the various sources.

Consequently, conventional methods in the field of solar arraymonitoring focus mainly on the collection of the output parameters fromthe overall solar array. Due to the wide variability of power output ofsuch systems, and the wide range of environmental conditions that affectthe power output, the output parameters from the overall system are notsufficient to verify whether the solar array is operating at peak powerproduction. Local disturbances, such as faulty installation, impropermaintenance, reliability issues and obstructions might cause localspower losses which are difficult to detect from overall monitoringparameters.

For further discussion of the above issues relating to distributed powersources and solar panels, the reader is highly encouraged to review thefollowing literature, which may or may not be prior art.

-   -   Cascade DC-DC Converter Connection of Photovoltaic        Modules, G. R. Walker and P. C. Sernia, Power Electronics        Specialists Conference, 2002. (PESCO2), Vol. 1 IEEE, Cairns,        Australia, pp. 24-29.    -   Topology for Decentralized Solar Energy Inverters with a Low        Voltage AC-Bus, Bjorn Lindgren.    -   Integrated Photovoltaic Maximum Power Point Tracking Converter,        Johan H. R. Enslin et al., IEEE Transactions on Industrial        Electronics, Vol. 44, No. 6, December 1997.    -   A New Distributed Converter Interface for PV Panels, R. Alonso        et al., 20th European Photovoltaic Solar Energy Conference, 6-10        Jun. 2005, Barcelona, Spain.    -   Intelligent PV Module for Grid-Connected PV Systems, Eduardo        Roman, et al., IEEE Transactions on Industrial Electronics, Vol.        53, No. 4, August 2006. Also in Spanish patent application        ES2249147.    -   A Modular Fuel Cell, Modular DC-DC Converter Concept for High        Performance and Enhanced Reliability, L. Palma and P. Enjeti,        Power Electronics Specialists Conference, 2007, PESC 2007, IEEE        Volume, Issue, 17-21 Jun. 2007 Page(s): 2633-2638. Digital        Object Identifier 10.1109/PESC.2007.4342432.    -   Experimental Results of intelligent PV Module for Grid-Connected        PV Systems, R. Alonso et al., Twenty first European Photovoltaic        Solar Energy Conference, Proceedings of the International        Conference held in Dresden, Germany, 4-8 Sep. 2006.    -   Cascaded DC-DC Converter Connection of Photovoltaic        Modules, G. R. Walker and P. C. Semia, IEEE Transactions on        Power Electronics, Vol. 19, No. 4, July 2004.    -   Cost Effectiveness of Shadow Tolerant Photovoltaic Systems,        Quaschning, V.; Piske, R.; Hanitsch, R., Euronsun 96, Freiburg,        Sep. 16-19, 1996.    -   Evaluation Test results of a New Distributed MPPT Converter, R.        Orduz and M. A. Egido, 22nd European Photovoltaic Solar Energy        Conference, 3-7 Sep. 2007, Milan, Italy.    -   Energy Integrated Management System for PV Applications, S.        Uriarte et al., 20th European Photovoltaic Solar Energy        Conference, 6-10 Jun. 2005, Barcelona, Spain.    -   U.S. Published Application 2006/0185727

SUMMARY

The following summary of the invention is provided in order to provide abasic understanding of some aspects and features of the invention. Thissummary is not an extensive overview of the invention, and as such it isnot intended to particularly identify key or critical elements of theinvention, or to delineate the scope of the invention. Its sole purposeis to present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented below.

According to aspects of the invention, there is provided a monitoringsystem employing one-way transmission. Collisions are avoided orminimized by a novel transmission timing scheme. The novel transmissionmethod also voids the necessity to synchronize the transmission of data.According to aspects of the invention, each transmission carries aunique ID of the data source. The data is collected and stored at acentral analysis system, and various analysis is performed on the datato ascertain the operation parameters of each transmission source and ofthe entire system. According to further aspects of the invention, amechanism for sending an interrupt message is provided. When a fault isdetected in any of the power sources, an interrupt message may be sentthat overrides all other messages, so that the fault may be detectedimmediately. According to aspects of the invention, all datatransmission is done using power line communication (PLC).Alternatively, other modes of transmission may be used, such as wirelessor dedicated transmission lines, such as Ethernet, RS232, RE485, etc.

According to aspects of the invention, a monitoring system fordistributed DC power installation is provided, comprising: a pluralityof power sources; a plurality of monitoring modules, each monitoringmodule associated with one of the power sources and collectingperformance data of the associated power source; a plurality oftransmitters, each transmitter associated with one of the monitoringmodules and transmitting the performance data; a plurality ofcontrollers, each associated with one of the transmitters andcontrolling transmission events according to elapsed time from timerinitialization. Each of the power sources may be connected to a powerline and wherein each transmitter transmits the performance data overthe power line. Each of the monitoring modules comprises: a currentmeasurement module for collecting the current data; and a voltagemeasurement module for collecting the voltage data. Each of themonitoring modules may further comprise a temperature sensor module forsensing the temperature data at the power source. Each of the monitoringmodules may further comprise an arc detection module for detectingarcing at the power source. Each of the monitoring modules may furthercomprise a timer, and wherein each controller initializes the timerwhenever the associated power source starts to generate power. Each ofthe monitoring modules may further comprise a randomizer for varyingtime increments for controlling transmission events. The monitoringsystem may further comprise a memory storing the performance dataaccumulated since timer initialization. The monitoring system mayfurther comprise: a central analysis station; and, a communicationtranslator for receiving the performance data from the monitoringmodules and transmitting the performance data to the central analysisstation. The central analysis station may analyze fault detection. Thecentral analysis station may compare measured power to expected powerdetermined based on external data. Each of the power sources maycomprise a solar panel. Each of the power sources may comprise a stringof serially connected solar panels. Each of the monitoring modules maycomprise a current measurement module for collecting current data. Themonitoring system may further comprise: a connection box for parallelcoupling all of the string of serially connected solar panels; and, avoltage measuring module measuring the voltage of the parallel coupling.The monitoring system may further comprise: a connection box forparallel coupling all of the string of serially connected solar panels;and, total current measuring module measuring the total current of theparallel coupling. The monitoring system may detect current leakage bycomparing output of the total current measuring module to the sum ofcurrent measuring modules of each of the monitoring modules.

According to aspects of the invention, a method for monitoringdistributed power harvesting systems including DC power sources isprovided, the method comprising: individually monitoring powergeneration at each of the DC power sources and, when power generationpasses a threshold at one of the DC power sources, performing the steps:initializing a timer for the power source; collecting performance datafor the power source; monitoring passage of time period of the timerand, when the time period reached a setup time, transmitting thecollected performance data to a central analysis station. Collectingperformance data may further comprise storing the performance data inmemory, and wherein transmitting the collected performance datacomprises transmitting the collected performance data accumulated sinceinitialization of the timer. Collecting performance data may comprisemeasuring at least one of output voltage and output current. The methodmay further comprise comparing performance data for at least one of theDC power sources to performance data from the same DC power source at adifferent time. The method may further comprise comparing performancedata for at least one of the DC power sources to performance data fromadjacent ones of the DC power sources. The method may further comprisecomparing performance data for at least one of the DC power sources toexpected performance data based on external parameters. Monitoringpassage of time period may further comprise introducing randomness tothe setup time. The method may further comprise serially connecting aplurality of solar panels to form each of the DC power sources.Transmitting the collected performance data may comprise sending thecollected performance data over a power line.

According to aspects of the invention, a distributed DC power harvestingsystem is provided, comprising: a plurality of solar panels seriallyconnected to form a string of panels coupled to a power line; at leastone monitoring module connected to the string of panels and gatheringperformance data from at least one solar panel, the monitoring modulecomprising: a transmitter for transmitting the performance data over thepower line; a controller for controlling transmission events of thetransmitter according to elapsed time from timer initialization; and, areceiving station coupled to the power line and receiving theperformance data from the transmitter. The receiving station may furthercomprise at least one of a voltage and current sensor. The receivingstation may further comprise a transmitter for relaying at least theperformance data received from the power line. The transmitter maycomprise a wireless transmitter. The monitoring module may comprise andleast one of: a current measurement module for collecting current datafrom at least one solar panel; and a voltage measurement module forcollecting voltage data from at least one solar panel. The monitoringmodule may further comprise a temperature sensor. The monitoring modulemay further comprise a timer, and wherein the controller initializes thetimer whenever an associated panel starts to generate power. Themonitoring module may further comprise a randomizer for varying timeincrements for controlling transmission events. The system may furthercomprise a memory storing the performance data accumulated since timerinitialization. The system may further comprise: one or more additionalstring of panels; a connection box for parallel coupling of the stringof panels and the one or more additional string of panels; and, avoltage measuring module measuring the voltage of the parallel coupling.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, exemplify the embodiments of the presentinvention and, together with the description, serve to explain andillustrate principles of the invention. The drawings are intended toillustrate major features of the exemplary embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of actualembodiments nor relative dimensions of the depicted elements, and arenot drawn to scale.

FIG. 1 illustrates a conventional solar power system.

FIG. 2 illustrates one serial string of DC sources and current versusvoltage characteristic curve for the solar panels.

FIG. 3A illustrates a monitoring module according to aspects of theinvention.

FIG. 3B is a flow chart illustrating a method for transmission of dataaccording to various aspects.

FIG. 4 shows a communication and analysis system, according to aspectsof the invention, being associated with the monitoring module of FIG.3A.

FIG. 5 shows a distributed power harvesting system, including amonitoring module, according to aspects of the invention.

FIG. 6 illustrates a solar system according to another embodiment of theinvention.

FIG. 7 illustrates a power converter, according to aspects of theinvention.

FIG. 8 illustrates a typical centralized solar field installation.

FIG. 9 illustrates a solar field installation implementing monitoringaccording to an embodiment of the invention.

FIG. 10 illustrates a solar field installation implementing monitoringaccording to another embodiment of the invention.

DETAILED DESCRIPTION

Aspects of the present invention provide a monitoring system for solarpanel system. The monitoring system includes modules that may beattached to each solar panel of the solar system. The monitoring modulewill monitor several parameters including, etc., panel voltage, panelcurrent, panel temperature, lighting conditions, spatial orientation(e.g., tilt), and other parameters. The information from each monitoringmodule may be transmitted to a central management unit together with aunique module ID. The transmission may be done over the powerlines, inwireless form, or with dedicated wiring—such as Ethernet, RS-232, RS-485or other. In one aspect of the invention, transmission is done as powerline communication in a one-way implementation. Collisions are avoidedor minimized by using a unique transmission timing mechanism.

The central management unit may analyze the data from all solar panels.The monitoring system can be implemented at the string level, at thepanel level or even at the cell level. The principle applicable at thepanel level monitoring may be applied for string level and cell level.Moreover, the innovative monitoring system may be used in smallinstallation, such as residential solar panel installations, and largeinstallations, such as large solar panel field power plants.

Analysis of the data may enable detection and pinpointing of most of thecommon failures associated with solar array power loss. Further, smartanalysis of current and historical data can also be used to suggestcorrective measures such as cleaning or replacing a specific portion ofthe solar array. The system can also detect normal power losses causedby environmental conditions and prevent costly and difficult solar arraytesting. Additionally, analysis of the data can lead to suggestion forenvironmental corrective actions. For example, it may suggest changingthe tilt or location of specific panels, or removing of obstacles thatblock the sun under certain conditions not realized at the time ofinstallation.

FIG. 3A shows a monitoring module according to aspects of the invention.The exemplary monitoring module 300, according to aspect of theinvention, is used to collect and transmit date from each solar panel,such as the solar panel 101 of FIG. 1. Data from all monitoring modulesis transmitted via a communication system to a central analysis station,which analyzes the data and displays the status of the solar array.

The monitoring module 300 includes several sub-modules. The sub-moduleswithin the monitoring module 300 include a current measurement module301, a microcontroller 302, a communication module 303, a voltagemeasurement module 304, a random access memory (RAM) module, anon-volatile RAM or NVRAM module 306, a temperature sensor 307 and oneor more external sensor interfaces 308.

The microcontroller module 302 is coupled to the other modules andcontrols the other modules. In one exemplary aspect shown in FIG. 3A,the current measurement module 301 is located in series with the inputand output ports to the monitoring module 300. The location of thecurrent measurement module 301 may vary depending on the type of currentmeasurement device used in the module. In the exemplary aspect shown,the voltage measurement module 304 is located in parallel across theinput port to the monitoring module 300. Voltage measurement devices areusually placed in parallel with the component whose voltage is beingmeasured. In the exemplary aspect shown, the communication module 303 isshown as located in parallel with the output ports of the monitoringmodule 300. There is no requirement for a particular location for thismodule and the location shown is arbitrary. The sensor modules whilecoupled to the microcontroller module 302, are not shown as coupled tothe input or output ports of the monitoring module 300. These sensormodules, however, may derive power from the panel connected to themonitoring module 300 and, therefore, may be located along a circuitpath from the input to the output ports of the monitoring module 300. Apower unit may be used to feed monitoring module 300. The power may bederived from one of many power sources, such as batteries or feed-infrom another location. In one embodiment the monitoring module 300 maybe fed from power harvested from the solar panel being monitored.

In various aspects of the invention, inclusion of some of the modules,such as the temperature sensor 307, is optional.

The monitoring module 300 can be implemented using discrete componentsor may be integrated to obtain an application specific integratedcircuit (ASIC).

The measurement modules 301, 304 and the sensor modules 307, 308 mayhave filter circuits and analog to digital conversion circuitsassociated with them. FIG. 3A shows low-pass filter and analog todigital conversion circuits 311, 314, 317, 318 each associated with acorresponding measurement and sensor module.

Current and voltage measurement modules 301, 304 are used to collectcurrent and voltage data. The collected data is transferred to themicrocontroller module 302. The microcontroller module 302 may be adigital state machine. The microcontroller stores the collectedinformation in its local RAM 305. Pre-defined data, stored in the NVRAMmodule 306, may be used to control the activity of the microcontroller302.

The data collected by the current and voltage measurement modules 301,304 and transferred to the microcontroller 302 may be subsequentlytransmitted to a central analysis station described below with respectto FIG. 4. The communication module 303 is used to transmit the datafrom the microcontroller 302 or from storage in RAM 305 to outside ofthe monitoring module 300.

The current measurement module 301 may be implemented by varioustechniques used to measure current. In one aspect of the invention, thecurrent measurement module 301 is implemented using a very low valueresistor. The voltage across the resistor will be proportional to thecurrent flowing through the resistor. In another aspect of theinvention, the current measurement module 301 is implemented usingcurrent probes which use the Hall Effect to measure the current througha conductor without the need to add a series resistor. After translatingthe current to voltage, the data passes through a low pass filter and isdigitized. The low-pass filter and the analog to digital converterassociated with the current measurement module 301 are shown as module311 in FIG. 3A. As with the voltage measurement module, care must betaken to choose the correct resolution and sample rate for the analog todigital converter. If the current sensing technique does not require aseries connection, then the monitoring module 300 may be connected tothe panel in parallel. For a parallel connection, there is no need todisconnect the panel during the connection.

In one aspect of the invention, the voltage measurement module 304 usessimple parallel voltage measurement techniques in order to measure thevoltage output of the solar panel. The analog voltage is passed througha low pass filter in order to minimize aliasing. The data is thendigitized using an analog to digital converter. The low-pass filter andthe analog to digital converter associated with the voltage measurementmodule 304 are shown as module 314 in FIG. 3A. The analog to digitalconverter 314 has sufficient resolution to correctly evaluate thevoltage from the solar panel. The low-pass filter makes it possible forlow sample rates to be sufficient for evaluating the state of the panel.

The optional temperature measurement module 307 enables the system touse temperature data in the analysis process. The temperature may beindicative of several types of failures and problems. Furthermore, thepanel temperature is a factor in the power output from the panel and inthe overall power production.

The one or more external sensor interfaces 308 enable connecting variousexternal sensors to the monitoring module 300. These sensors areoptional and may be used where they enable enhanced analysis of thestate of the solar array. Examples of external sensors that may be usedat the external sensor interfaces 308, include ambient temperaturesensor, solar irradiance sensors, spatial orientation such as tiltsensor, sensors from neighboring panels and the like. When a type ofsensor is regularly used, then it may be integrated into the monitoringmodule 300 instead of being an external component.

The microcontroller module 302 manages the monitoring process. The tasksperformed by the microcontroller module 302 includes gatheringinformation from the current and voltage measurement modules 301, 304,storing the information in local memory 305, 306 and transmitting thestored information to outside of the monitoring module 300. Themicrocontroller module 302 uses the information stored in memory inorder to control its operation. This operating information may be storedin the non-volatile memory of the NVRAM module 306, to preserve theinformation even when power-loss occurs. Information in the NVRAM module306 may include information about the microcontroller module 302 such asthe serial number, the type of communication bus used, the status updaterate and the ID of the central analysis station to which the data istransmitted. This information may be added to the parameters collectedby the measurement modules 301, 304 before transmission out of themonitoring module 300.

The installation process of the monitoring module 300 includesconnecting each of the monitoring modules 300 to a panel such as thesolar panel 101 of FIG. 1 or the solar panel 505 of FIG. 5. Themeasurement features of the monitoring module 300 may be used to ensurethat the panel and the monitoring module are properly connected and torecord the serial number of the monitoring module 300 or themicrocontroller within the monitoring module. The measurement features301, 304, or other sensors, such as GPS, tilt etc., may also be used todetermined physical location of the connection and the array connectiontopology. These parameters may be used by an analysis software at thecentral analysis station 403 to detect problems in the solar panels andthe array.

The monitoring module 300 may be installed during the installation ofthe solar array or retrofitted to an existing installation. In bothcases the monitoring module may be connected to the panel junctionconnection box or to the cables between the panels. The monitoringmodule may be provided with the connectors and cabling needed to enableeasy installation and connection to the panels and cables.

The monitoring module 300 shown in FIG. 3A collects current, voltage andsome other optional types of data from each of the panels in adistributed DC power harvesting system. Data from each panel issubsequently transmitted for analysis. The communication module 303connects the microcontroller module 302 to the communication bus that isdescribed below with reference in FIG. 4. The communication from eachmonitoring module 300 is performed using conventional power linecommunication technique (also known as power line carrier). However, aunique transmission timing is utilized in order to avoid or minimizecollisions. This technique will be explained with reference to aspecific example of a monitor connected to a solar panel.

When the solar panel “wakes”, i.e., starts to receive sun light andgenerate output power, the monitor initializes a timer to time to. Themonitor may or may not send data at the initialization time. Then, themonitor collects data continuously, but transmits collected data onlyafter a given period has past from t₀ or from the last transmission. Forexample, the monitor may transmit data every 15 minutes. Since thepanels are spatially separated, they will most likely wake at differenttimes, introducing randomness to the transmission time, so that eachpanel would transmit according to its own timer. That is, each monitorwould transmit data at:

t ₀ +xC,

where x is a whole natural number and Cis a set constant, say 15minutes. However, for each panel t₀ may be at a different time everymorning

As can be appreciated from the above, using the wake up time of thepanel to initiate the timer introduces a measure of randomness thathelps avoid collisions. According to another embodiment of theinvention, another measure of randomness is introduced in the counter.For example, the transmission time may be calculated as t₀+xC+E, where Eis a random number provided by a random number generator, etc.Alternatively, the transmission time may be calculated as t0+x(C+E).Notably, the random number should be generated separately to each moduleto prevent the chance that two panels wake at the same time andincrement the counter at the same rate, thereby colliding on eachtransmission attempt. This random element may be reintroduced for eachtime a transmission is sent. Other methods of introducing randomness mayalso be used.

FIG. 3B is a flow chart illustrating a method for transmission of databy the monitor 300 of FIG. 3A. At step 340 it is checked whether thepanel has awaken (i.e., receives light and generates power at apredetermined level). If so, the process proceeds to step 342 where thetimer is initialized and the counting is started. Data, such as current,voltage, temperature, illumination, power output, etc., is thencollected and stored, e.g., in RAM 305, at step 344, which continues solong as the timer progresses and the panel has not gone to sleep (352).As explained above, optionally a further randomization is introduced,which is shown by step 346. Then at step 348 it is determined whetherthe time for transmitting data has been reached and, if so, the data istransmitted at step 350. In this particular example, the data that istransmitted is the data accumulated since initialization of the timer.However, other methodologies may be implemented. For example, the datamay be data accumulated since last transmission or current data reading.At step 352 it is checked whether the panel assumed the sleep mode,e.g., illumination or power generation is below a threshold. If so, theprocess ends. Otherwise, counting and transmission of data continues.

The above schemes minimize or avoid collisions. However, if a collisiondoes occur, since the transmission is only one way, the central systemwould not get the data and would not know what data was lost, and thesending monitors would also have no way of knowing that the data neverreached the central system. As a result, when the central systemanalyzes the data and compares data from one panel to another, errorsmay be introduced if some data transmission was lost due to collision.For example, if the central unit tries to compare power generated byseveral panels between 1 pm and 2 pm, the comparison would be inaccurateif data from two or more panels collided at 1:30 pm and is missing fromthe calculation.

To avoid this problem, a scheme is adopted wherein the data isaccumulated at each monitor. Then, at each transmission, the accumulatedtotal value of the data is transmitted. For example, at time t₁₅ thepower generated from wake to wake plus 15 minutes is transmitted. Attime ho the power generated from wake to wake plus 30 minutes istransmitted, and so on. In this way, even if one or more transmissionwas not received by the central unit, the central unit can reconstructthe missing data by, for example, extrapolating it from the data fromall of the transmissions that were received. Similar extrapolation maybe done in order to put data that arrived at different times fromdifferent panels in order to compare between panels on a unifiedtime-base. E.g. Curves of power production from the monitors could beextrapolated for each panel based on the data points that arrived, andthen these curves could be compared in order to detect power anomaliesor other problems and phenomena.

According to a further aspect of the invention, an interrupt message maybe sent, which overrules all other messages. An interrupt message may besent by any monitoring module 300, for example, whenever a rapidcorrective action may be required. This may be when power dropssuddenly, as due to malfunction, panel breakage due to hail storms orother cause, etc. The interrupt message may be sent at any time,regardless of the counter's position. In connection with the interruptmessage, according to an aspect of the invention a wide band noisedetector is implemented in the module 300. When the wideband noisedetector detects noise above a certain threshold, it sends an interruptmessage. Notably, this feature is implemented to identify arcing thatmay be caused due to an open connection in the system. That is, sincethe system voltage is relatively high, e.g., 400-600V, if a connectionbecomes separated, and potential may arc through the air. Such arcingcan be detected as wideband noise. The wideband noise detector may beimplemented as part of the controller 102, as shown in FIG. 3A, or as aseparate unit.

Additionally, to assist in locating faults and deleterious conditions,each monitor has a unique ID, which is transmitted together with thedata. In this way, the central unit can easily monitor each panelindividually and the physical location of the panel corresponding toeach data stream can be easily ascertained. Thus, for example, if everyday at 2 pm there is power drop at one or more panels, their physicallocation can be easily ascertained by using the unique ID transmittedwith the data. Then the status of the panels can be evaluated to seewhether there is an obstacle that obscures the sun every day at 2 pm.Furthermore, if a geographic information sensor (such as a GPS) isattached to the monitoring module, it could directly transmit itslocation so the obstruction may be found and removed.

The central analysis unit may also use the ID information to performdata analysis by comparing the data from the particular panel toexpected data obtained from external sources. That is, if the centralanalysis system knows the location, temperature, tilt, etc., of thepanel having the particular ID, it may calculate expected power fromthis panel at the current prevailing conditions. If the data receivedfrom the panel substantially deviates from the expected power output, itmay determine that the panel is faulty or some factors cause it to losepower. This is especially a beneficial feature in the topology of theembodiment described herein, since the maximum power point tracking isperformed on an individual panel basis, so the power obtained should becommensurable with the expected power. That is, there is no errorintroduced due to tracking maximum power point on an average of severalpanels.

FIG. 4 shows a communication and analysis system, according to aspectsof the invention, being associated with the monitoring module of FIG.3A. FIG. 4 shows a system used for collecting data from each of thepanels in a distributed power system and subsequent analysis ofcollected data. The system of FIG. 4 includes a number of panels 401that generate power. Each panel includes a monitoring module such as themonitoring module 300. Data collected by the monitoring modules at thepanels 402 are communicated by a module communication bus 404 to acommunication translator 401. The communication translator 401 sends thedate to a central analysis station 403 via a communication link 403. Thecentral analysis station 403 receives the data that is transmitted viathe communication bus 404, analyzes the data and displays the status ofthe panels corresponding to the time the data was collected.

In FIG. 4, one module communication bus 404 is shown for transmittingdata from the monitoring modules 300 from a number of panels 402. Thedata may be transmitted on a single bus in the manner described abovewhich eliminates or minimizes collisions. However, other transmissionmethods may be used. For example, the data from several panels may bemultiplexed on the same module communication bus. Alternatively, eachmonitoring module 300 includes a separate module communication bus 404.The module communication buses 404 from the different monitoring modulescarry the data from each monitoring module 300 to the communicationtranslator 401.

The module communication bus 404 can be implemented in different ways.In one aspect of the invention, an off-the-shelf communication bus suchas Ethernet, RS232 or RS485 is used. Using an off-the-shelfcommunication bus simplifies the design of the communication module 303of the monitoring module 300 but requires separate cables. Other methodssuch as wireless communications or power line communications may also beused. When wired communication is used between the monitoring modules300 and the communication translator 401, the communication translator401 may be located in close physical proximity to the panels to reducethe length of the module communication bus 404 or buses. When wirelesscommunication is used between the monitoring modules 300 and thecommunication translator 401, the communication translator 401 need notbe in close physical proximity to the panels.

The communication translator 401 is used to convert the modulecommunication bus or buses 404 to a standard communication protocol andphysical layer. This enables receiving data from the monitoring module300 on various data terminals, such as a computer or PDA. The centralanalysis station 403 may then be implemented as a software that is runon a standard PC, an embedded platform or a proprietary device.

In one aspect of the invention, unidirectional power line communicationis used from the monitoring modules 300 to the central analysis station403. With unidirectional communication, a mechanism for preventingcross-talk between the monitoring modules 300 may be provided. Such amechanism may be implemented in the form of transmitting data from eachof the monitoring modules 300 at preset times as explained with respectto FIG. 3B. In one aspect of the invention, a collision detectionalgorithm may be used to ensure the data is received without collisionsat the central analysis station 403.

In one aspect of the invention, bidirectional communication is usedbetween the central analysis station 403 and the monitoring modules 300.With bidirectional communication, the central analysis station 403 mayproactively request the data collected by one or more of the monitoringmodules 300.

The collected data is analyzed at the central analysis station 403. Byanalyzing the information from each of the monitoring modules, manycauses for power losses can be detected. For example, when energyproduction from a panel is low on some hours of the day while theadjacent panels produce the same power on all hours, the low performancepanel is probably shaded during the low production hours. Panels thatproduce little power in comparison to their adjacent panels might beconstantly shaded, soiled or installed incorrectly. Comparison of thepower output of each panel with its corresponding power output a yearearlier may indicate that the output has diminished due to dust or soilcollected on the panel. Additional data may be gathered from outsidesources in order to monitor and evaluate the power production of thearray. E.g. irradiance data from satellites, weather data fromterrestrial stations, RADAR systems or satellites, or weather andirradiance forecasts based on historical data or computerized models,and so forth. Many more heuristics and algorithmic methods may be usedto detect problems and help the owner of the system to pinpoint problemsin the array. Having the unique ID transmitted with the data helpsidentify the panels and their physical location.

FIG. 5 shows a distributed power harvesting system, including amonitoring module, according to aspects of the invention. Configuration50 enables connection of multiple power sources, for example solarpanels 501 to a single power supply. The series connection of all of thesolar panels is connected to an inverter 504. A central analysis station500 is shown that is in communication with the monitoring modules 300coupled to each of the solar panels 501. Station 500 may be incorporatedinto the inverter 504 or may be an independent unit.

In configuration 50, each solar panel 501 is connected to a separatepower converter circuit 505. Power converter circuit 505 adaptsoptimally to the power characteristics of the connected solar pane 1501and transfers the power efficiently from input to output. Powerconverters 505 can be buck converters, boost converters, buck/boostconverters, flyback or forward converters. The converters 505 may alsocontain a number of component converters, for example a serialconnection of a buck and a boost converter.

Each converter 505 includes a control loop that receives a feedbacksignal, not from the output current or voltage, but rather from theinput coming from the solar panel 501. An example of such a control loopis a maximum power point tracking (MPPT) loop in solar arrayapplications. The MPPT loop in the converter locks the input voltage andcurrent from each solar panel 501 to its optimal power point. The MPPTloop of the converter 505 operates to perform maximum power pointtracking and transfers the input power to its output without imposing acontrolled output voltage or output current.

Each converter 505 may include a monitoring module according to theaspects of the invention. For example, each converter 505 may includethe monitoring module 300 of FIG. 3A. The communication link between themonitoring modules 300 and the central analysis station 500 may bewireless or wired. If wired, the connection may be done to each unit 505individually or centrally via inverter 504. Note that there isadditional value in monitoring the panels output when coupling it withMPPT tracking power converter 505, since this guaranties that the powermonitored is at maximum power point, and therefore low power readingsignify a real problem and are not merely a false-alarm that resultsfrom the current draw from a central inverter, which may not be optimalfor each panel. Converters 505 can be connected in series or in parallelto form strings and arrays.

Conventional DC-to-DC converters have a wide input voltage range at thesolar panel side and an output voltage predetermined and fixed oninstallation. In these conventional DC-to-DC voltage converters, thecontroller monitors the current or voltage at the input, and the voltageat the output. The controller determines the appropriate pulse widthmodulation (PWM) duty cycle to fix the input voltage to thepredetermined value decreasing the duty cycle if the input voltage dropswhile varying the current extracted from the input. In converters 505,according to embodiments of the present invention, the controllermonitors the voltage and current at its input and determines the PWM insuch a way that maximum power is extracted, dynamically tracking themaximum point. In embodiments of the present invention, the feedbackloop is closed on the input power in order to track maximum power ratherthan closing the feedback loop on the output voltage as performed byconventional DC-to-DC voltage converters.

The outputs of converters 505 are series connected into a single DCoutput into the inverter 504, which converts the series connected DCoutput to an alternating current power supply. If the output is notrequired to be AC, the inverter may be omitted, or other load, such as acentral DC/DC converter or battery charger may be used instead.

The circuit of FIG. 5 provides maximum power available during continuousoperation from each solar panel 501 by continuously performing MPPT onthe output of each solar panel to react to changes in temperature, solarradiance, shading or other performance deterioration factors of eachindividual solar panel 501. As shown in FIG. 1, conventional solutionsfor combining power, perform MPPT on strings 103 or arrays of solarpanels 101. As a result of having a separate MPPT circuit in eachconverter 505, and for each solar panel 501, in the embodiments of thepresent invention, each string 503 in the embodiment shown in FIG. 5 mayhave a different number of panels 501 connected in series. Furthermorepanels 501 can be installed in different directions, as solar panels 501do not have to be matched and partial shading degrades the performanceof only the shaded panel. According to embodiments of the presentinvention, the MPPT circuit within the converter 505 harvests themaximum possible power from panel 501 and transfers this power as outputregardless of the parameters of other solar panel 501.

FIG. 6 illustrates a solar system according to another embodiment of theinvention. The embodiment of FIG. 6 is similar to that of FIG. 5, inthat panels 601 are connected in series to form strings 603. The strings603 are then connected in parallel to inverter 604. The inverter 604includes a central analysis station 600 that receives data fromreporting modules within converters 605. Central station 600 alsoreceives data from reporting module 606, which provides data relating tothe entire power delivered from all of the panels.

FIG. 7 illustrates a power converter, according to aspects of theinvention. FIG. 7 highlights, among others, a monitoring and controlfunctionality of a DC-to-DC converter 705, according to embodiments ofthe present invention. A DC voltage source 701 is also shown in thefigure. Portions of a simplified buck and boost converter circuit areshown for the converter 705. The portions shown include the switchingtransistors 728, 730, 748 and 750 and the common inductor 708. Each ofthe switching transistors is controlled by a power conversion controller706.

The power conversion controller 706 includes the pulse-width modulation(PWM) circuit 733, and a digital control machine 730 including aprotection portion 737. The power conversion controller 706 is coupledto microcontroller 790, which includes an MPPT module 719, and may alsooptionally include a communication module 709, a monitoring and loggingmodule 711, and a protection module 735.

A current sensor 703 may be coupled between the DC power source 701 andthe converter 705, and output of the current sensor 703 may be providedto the digital control machine 730 through an associated analog todigital converter 723. A voltage sensor 704 may be coupled between theDC power source 701 and the converter 705 and output of the voltagesensor 704 may be provided to the digital control machine 730 through anassociated analog to digital converter 724. The current sensor 703 andthe voltage sensor 704 are used to monitor current and voltage outputfrom the DC power source, e.g., the solar panel 701. The measuredcurrent and voltage are provided to the digital control machine 730 andare used to maintain the converter input power at the maximum powerpoint.

The PWM circuit 733 controls the switching transistors of the buck andboost portions of the converter circuit. The PWM circuit may be adigital pulse-width modulation (DPWM) circuit. Outputs of the converter705 taken at the inductor 708 and at the switching transistor 750 areprovided to the digital control machine 730 through analog to digitalconverters 741, 742, so as to control the PWM circuit 733.

A random access memory (RAM) module 715 and a non-volatile random accessmemory (NVRAM) module 713 may be located outside the microcontroller 706but coupled to the microcontroller 706. The unique ID and other relateddata, such as serial number, manufacturer, manufacturing date, etc., maybe stored in the NVRAM. A temperature sensor 779 and one or moreexternal sensor interfaces 707 may be coupled to the microcontroller706. The temperature sensor 779 may be used to measure the temperatureof the DC power source 701. A physical interface 717 may be coupled tothe microcontroller 706 and used to convert data from themicrocontroller into a standard communication protocol and physicallayer. An internal power supply unit 739 may be included in theconverter 705.

In various aspects of the invention, the current sensor 703 may beimplemented by various techniques used to measure current. In one aspectof the invention, the current measurement module 703 is implementedusing a very low value resistor. The voltage across the resistor will beproportional to the current flowing through the resistor. In anotheraspect of the invention, the current measurement module 703 isimplemented using current probes which use the Hall Effect to measurethe current through a conductor without adding a series resistor. Aftertranslating the current to voltage, the data may be passed through a lowpass filter and then digitized. The analog to digital converterassociated with the current sensor 703 is shown as the AID converter 723in FIG. 7. Aliasing effect in the resulting digital data may be avoidedby selecting an appropriate resolution and sample rate for the analog todigital converter. If the current sensing technique does not require aseries connection, then the current sensor 703 may be connected to theDC power source 701 in parallel.

In one aspect of the invention, the voltage sensor 704 uses simpleparallel voltage measurement techniques in order to measure the voltageoutput of the solar panel. The analog voltage is passed through a lowpass filter in order to minimize aliasing. The data is then digitizedusing an analog to digital converter. The analog to digital converterassociated with the voltage sensor 704 are shown as the AID converter724 in FIG. 7. The AID converter 724 has sufficient resolution togenerate an adequately sampled digital signal from the analog voltagemeasured at the DC power source 701 that may be a solar panel.

The current and voltage data collected for tracking the maximum powerpoint at the converter input may be used for monitoring purposes also.An analog to digital converter with sufficient resolution may correctlyevaluate the panel voltage and current. However, to evaluate the stateof the panel, even low sample rates may be sufficient. A low-pass filtermakes it possible for low sample rates to be sufficient for evaluatingthe state of the panel. The current and voltage date may be provided tothe monitoring and logging module 711 for analysis.

The temperature sensor 779 enables the system to use temperature data inthe analysis process. The temperature is indicative of some types offailures and problems. Furthermore, in the case that the power source isa solar panel, the panel temperature is a factor in power outputproduction.

The one or more optional external sensor interfaces 707 enableconnecting various external sensors to the converter 705. Externalsensors are optionally used to enhance analysis of the state of thesolar panel 701, or a string or an array formed by connecting the solarpanels 701. Examples of external sensors include ambient temperaturesensors, solar radiance sensors, and sensors from neighboring panels.External sensors may be integrated into the converter 705 instead ofbeing attached externally.

In one aspect of the invention, the information acquired from thecurrent and voltage sensors 703, 704 and the optional temperature andexternal sensors 705, 707 may be transmitted to a central analysisstation for monitoring, control, and analysis using the communicationsinterface 709. The central analysis station is not shown in the figure.The communication interface 709 connects a microcontroller 706 to acommunication bus. The communication bus can be implemented in severalways. In one aspect of the invention, the communication bus isimplemented using an off-the-shelf communication bus such as Ethernet orRS422. Other methods such as wireless communications or power linecommunications may also be used. If bidirectional communication is used,the central analysis station may request the data collected by themicrocontroller 706. Alternatively or in addition, the informationacquired from sensors 703, 704, 705, 707 is logged locally using themonitoring and logging module 711 in local memory such as the RAM 715 orthe NVRAM 713.

Analysis of the information from sensors 703, 704, 705, 707 enablesdetection and location of many types of failures associated with powerloss in solar arrays. Smart analysis can also be used to suggestcorrective measures such as cleaning or replacing a specific portion ofthe solar array. Analysis of sensor information can also detect powerlosses caused by environmental conditions and prevent costly anddifficult solar array testing.

Consequently, in one aspect of the invention, the microcontroller 706simultaneously maintains the maximum power point of input power to theconverter 705 from the attached DC power source or solar panel 701 basedon the MPPT algorithm in the MPPT module 719 and manages the process ofgathering the information from sensors 703, 704, 705, 707. The collectedinformation may be stored in the local memory 713, 715 and transmittedto an external central analysis station. In one aspect of the invention,the microcontroller 706 uses previously defined parameters stored in theNVRAM 713 in order to operate. The information stored in the NVRAM 713may include information about the converter 705 such as serial number,the type of communication bus used, the status update rate and the ID ofthe central analysis station. This information may be added to theparameters collected by the sensors before transmission.

The converters 705 may be installed during the installation of the solararray or retrofitted to existing installations. In both cases, theconverters 705 may be connected to a panel junction connection box or tocables connecting the panels 701. Each converter 705 may be providedwith the connectors and cabling to enable easy installation andconnection to solar panels 701 and panel cables.

In one aspect of the invention, the physical interface 717 is used toconvert to a standard communication protocol and physical layer so thatduring installation and maintenance, the converter 705 may be connectedto one of various data terminals, such as a computer or PDA. Analysismay then be implemented as software which will be run on a standardcomputer, an embedded platform or a proprietary device.

The installation process of the converters 705 includes connecting eachconverter 705 to a solar panel 701. One or more of the sensors 703, 704,705, 707 may be used to ensure that the solar panel 701 and theconverter 705 are properly coupled together. During installation,parameters such as serial number, physical location and the arrayconnection topology may be stored in the NVRAM 713. These parameters maybe used by analysis software to detect future problems in solar panels701 and arrays.

When the DC power sources 701 are solar panels, one of the problemsfacing installers of photovoltaic solar panel arrays is safety. Thesolar panels 701 are connected in series during the day when there issunlight. Therefore, at the final stages of installation, when severalsolar panels 701 are connected in series, the voltage across a string ofpanels may reach dangerous levels. Voltages as high as 600V are commonin domestic installations. Thus, the installer faces a danger ofelectrocution. The converters 705 that are connected to the panels 701may use built-in functionality to prevent such a danger. For example,the converters 705 may limit the output voltage to a safe level until apredetermined minimum load is detected. Only after detecting thispredetermined load, the microcontroller 706 ramps up the output voltagefrom the converter 705.

Another method of providing a safety mechanism is to use communicationsbetween the converters 705 and the associated inverter for the string orarray of panels. This communication, that may be for example a powerline communication, may provide a handshake before any significant orpotentially dangerous power level is made available. Thus, theconverters 705 would wait for an analog or digital signal from theinverter in the associated array before transferring power to inverter.

The above methodology for monitoring, control and analysis of the DCpower sources 701 may be implemented on solar panels or on strings orarrays of solar panels or for other power sources such as batteries andfuel cells.

The innovative monitoring described so far may be implemented in anysolar panel installation, but is particularly beneficial for residentialand relatively small installations. On the other hand, for largeinstallations, such as, e.g., 025 megawatt solar field and larger,implementing monitoring on each panel may prove to be prohibitivelyexpensive. Accordingly, the monitoring solution provided herein may bemodified for such applications.

FIG. 8 illustrates a typical centralized solar field installation. InFIG. 8, a large field installation is formed by connecting several solarpanels 805 in series so as to form a string 810. Normally 8-20 panels805 are serially connected to form one string 810. Then, severalstrings, e.g., eight or twelve strings are connected in parallel to forma cluster 815. Several clusters are then connected together in a supercluster junction box 820, sometimes called a combiner box, to form asuper cluster. The super cluster may be connected to a central inverter,or to other super clusters. According to the prior art, monitoring ofsuch a system is done by measuring current and voltage at the output ofthe super cluster. However, such monitoring detects only majormalfunctions and fails to detect smaller problems that, if corrected,can lead to higher efficiency. On the other hand, it has been proposedto provide a monitor at each panel and utilize master-slave arrangementto obtain performance data from each panel. However, such an arrangementis costly both in terms of the additional cost for each monitor on eachpanel (there are normally hundreds to tens of thousands of panels inlarge field installations) and in terms of complexity of thetransmission requirements. For further background information the readeris directed to U.S. Patent Publication 2006/0162772.

FIG. 9 illustrates a centralized solar field installation implementingmonitoring according to an embodiment of the invention. The system 900is arranged with panels 905 serially connected to strings 910, which areconnected in parallel to form clusters 915, which are in tum connectedto a super cluster junction box 920. In the embodiment of FIG. 9 onemonitor 925 is installed for each string 910 of serially connectedpanels 905. The monitor 925 may be the same monitor 300 as in FIG. 3A.On the other hand, in one embodiment the monitor 925 includes only acurrent probe and transmission means, which may be similar to that ofmonitor 300. While in FIG. 9 the monitor 925 is shown connected to thefirst panel 905, it may be connected to any of the serially connectedpanels in the string 910. Additionally, one voltage monitor 930 isconnected at the super cluster junction box 920. A power unit may beused to feed monitors 925 and 930. The power may be derived from one ofmany power sources, such as batteries or feed-in from another location.In one embodiment monitors 925 and 930 may be fed from power harvestedfrom the cable running through them—the solar panel being monitored inthe case of monitor 925, and the current from one or more entireclusters 915 in the case of combiner box 920.

With the arrangement of FIG. 9, since each string 910 is connected inparallel to all other strings at the super cluster junction box 920, thevoltage measured by the voltage monitor 930 indicates the voltage ofeach string 910. The voltage measurement is sent from the box 920 andthe current is sent from each string separately to a central monitoringsystem (not shown). Alternatively, monitors 925 may send their data overpower line communication or in other means to monitor 930, which thenaggregates the data and sends it to central monitoring system. Themonitor 930 may transmit the data it receives together with any data itmonitors itself to a central monitoring station (not shown) using othertransmission methods, such as Ethernet, wireless communication (WiFi,ZigBee, etc.) via one-way or two way communication, as illustrated bythe arrow 955. Consequently, the central monitoring station cancalculate the power production from each string. Such monitoring is moresensitive to power drops and other malfunctions at each string. Thisenables improved identification of failing or malfunctioning panelswithout the expense of installing monitor at each panel.

Additionally, rather than utilizing complicated master slavearrangement, in this embodiment the monitors 925 send the data using thepower line communication via unidirectional communication method asexplained above with respect to FIGS. 3A and 3B. This way, no dedicatedbus is required and collisions are avoided by using the randomizingmechanism discussed above. Since solar fields may be very large andinclude many thousands or transmitting monitors, it is beneficial toprevent data transmitted in one part of the field to interfere with datatransmitted in other parts. In an aspect of the invention, such aseparation might me done by introducing capacitors 960 between theoutput terminals of each super cluster combiner box 920. This capacitor920 is used to attenuate the PLC signaling in the super-cluster, andprevent interference with other super-clusters.

FIG. 10 illustrates a solar field installation implementing monitoringaccording to another embodiment of the invention. The embodiment of FIG.10 is similar to that of FIG. 9, except that a current monitor 1035 isadded to measure the total current provided by each cluster 1010. Thecurrent measured at current monitor 1035 should be the sum of thecurrent measurements of all of the monitors 1025. That is, the readingof current monitor should be commensurable to the sum of the readingreported by all of the monitors 1025 (less transmission losses). If anabnormal discrepancy is detected, then it means that at least one of thestrings 1010 has problem with current delivery. This may be due to afaulty connector, bad cable isolation, or other factors. Thus, theproblem is detected and could easily be pinpointed and fixed.

Embodiments of the invention, such as those described above, provide agreater degree of fault tolerance, maintenance and serviceability bymonitoring, controlling, logging and/or communicating the performance ofeach solar panel 501, or strings of solar panels 503. A microcontrollerused in the MPPT circuit of the converter 505, may include themonitoring module 300 of FIG. 3A. Then, this microcontroller may also beused to perform the monitoring, logging and communication functions.These functions allow for quick and easy troubleshooting duringinstallation, thereby significantly reducing installation time. Thesefunctions are also beneficial for quick detection of problems duringmaintenance work. Furthermore, by monitoring the operation of each partof the system, preventive maintenance may be performed in a timelymanner to avoid downtime of the system.

The present invention has been described in relation to particularexamples, which are intended in all respects to be illustrative ratherthan restrictive. Those skilled in the art will appreciate that manydifferent combinations of hardware, software, and firmware will besuitable for practicing the present invention. Moreover, otherimplementations of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims and theirequivalents.

1-36. (canceled)
 37. An apparatus, comprising: a power source connectedto a power line; a monitoring module comprising a timer, wherein themonitoring module is configured to collect performance data of the powersource; a transmitter configured to transmit the performance data overthe power line; and a controller configured to control the transmitterto transmit the performance data when an elapsed time period frominitialization of the timer reaches a transmission time period of thetransmitter.
 38. The apparatus of claim 37, wherein the power line isshared with other power sources.
 39. The apparatus of claim 37, whereinthe monitoring module further comprises a randomizer configured toinclude random time increments in the transmission time period of thepower source.
 40. The apparatus of claim 37, further comprising: acurrent measurement module configured to collect current data of thepower source; and a voltage measurement module configured to collectvoltage data of the power source.
 41. The apparatus of claim 37, furthercomprising a temperature sensor configured to sense temperature data ofthe power source.
 42. The apparatus of claim 37, wherein the monitoringmodule further comprises an arc detection module configured to detectarcing at the power source.
 43. The apparatus of claim 37, furthercomprising a memory configured to store the performance data accumulatedsince the initialization of the timer.
 44. The apparatus of claim 37,further comprising: a communication module configured to transmit theperformance data over the power line to a communication translator. 45.A method, comprising: monitoring power generation of a power source;when power generation of the power source passes a threshold,initializing a timer and collecting performance data of the powersource; monitoring an elapsed time period of the timer frominitialization of the timer; determining whether the elapsed time periodof the timer has reached a transmission time period of the power source;and in response to determining that the elapsed time has reached thetransmission time period of the power source, transmitting the collectedperformance data over a power line.
 46. The method of claim 45, furthercomprising: generating a random time increment; and determining thetransmission time period by adding the random time increment to aperiodic transmission time of the power source.
 47. The method of claim45, wherein transmitting the collected performance data over a powerline comprises: transmitting, to a communication translator incommunication with a plurality of power sources, the collectedperformance data over a power line shared with the plurality of powersources.
 48. The method of claim 45, wherein collecting performance datafurther comprises storing the performance data in memory, and whereintransmitting the collected performance data comprises transmitting thecollected performance data accumulated since a previous transmission ofperformance data.
 49. The method of claim 45, wherein collectingperformance data comprises measuring at least one of output voltage andoutput current.
 50. The method of claim 45, wherein transmitting thecollected performance data over a power line comprises: transmitting thecollected performance data with a unique identifier of the power sourceover the power line.
 51. The method of claim 45, further comprising:detecting for wideband noise; and in response to detecting widebandnoise above a threshold, transmitting an interrupt message.
 52. Asystem, comprising: a plurality of panel units connected to acommunication line, wherein each panel unit comprises: a power source; amonitoring module configured to collect performance data of the powersource; a transmitter configured to transmit the performance data overthe communication line; and a controller configured to control thetransmitter to transmit the performance data using the communicationline; and a communication translator configured to receive theperformance data from each of the plurality of panel units over thecommunication line, wherein the controller of each panel unit isconfigured to avoid transmission collisions with controllers of otherpanel units.
 53. The system of claim 52, wherein the monitoring modulecomprises a timer, and wherein the controller is configured to transmitthe performance data based on an elapsed time period of the timer and atransmission time period associated with the panel unit of thecontroller.
 54. The system of claim 53, wherein the monitoring modulefurther comprises a randomizer configured to include random timeincrements in the transmission time period.
 55. The system of claim 52,wherein the communication line comprises a power line.
 56. The system ofclaim 52, further comprising: a central analysis station configured todetect for faults, wherein the communication translator is configured totransmit the performance data to the central analysis station.